1. Field of the Invention
The present invention relates to a semiconductor optical element, an integrated semiconductor optical element, and a semiconductor optical element module used for optical communication or the like.
2. Description of the Related Art
In optical communications, in order to compensate for attenuation of an optical signal in an optical fiber as an optical transmission path or loss of the optical signal due to optical components, an optical amplifier is used. As the optical amplifier, a semiconductor optical amplifier is promising in terms of miniaturization and integration.
As the semiconductor optical amplifiers, there are a resonance type semiconductor optical amplifier which actively uses optical resonance by reflection on an optical waveguide facet and a traveling wave type semiconductor optical amplifier where the reflection on the facet is removed to the utmost. The traveling wave type semiconductor optical amplifier has an advantage in that wavelength dependency of amplification characteristics is small.
In a semiconductor optical element including a traveling wave type semiconductor optical amplifier, in order to reduce reflection on a facet, for example, as a cleaved plane, in some cases, a structure where an optical waveguide in the vicinity of the facet is inclined with respect to the facet may be employed. In this case, a structure where a curved waveguide is installed in the vicinity of the facet, the optical waveguide at the facet is inclined with respect to the facet, and optical waveguides in the other portions are perpendicular to the facet may be employed (for example, refer to Japanese Laid-open Patent Publication No. 2001-111177).
On the other hand, the semiconductor optical amplifier has a problem in that the output power may be likely to be saturated if the optical power is large. In order to solve the problem and to increase the output optical power, in some cases, a flared structure of which waveguide width is widened as it goes to an output-side facet may be used (for example, refer to Japanese Laid-open Patent Publication No. 05-067845).